What is the midline equation of $y=-9\cos\left(\dfrac{\pi}{2} x-6\right)+8$ ? $y=$
Solution: Midline in sinusoids of the form $y=a\cos(bx+c)+d$ Graphically, the midline of a sinusoidal function is the horizontal line that passes exactly in the middle of its extreme values. The midline equation of a sinusoid of the form $y={a}\cos(bx + c) + {d}$ is equal to $y={d}$. [How can we justify this given our graphical understanding of midline?] Finding the midline The midline equation of $y = -9\cos\left(\dfrac{\pi}{2} x-6\right)+{8}$ is $y={8}$.